Since its foundation by the Romans in 15 BC, Aventicum, today Avenches, was the capital of the tribe of Helvetii. Today it is one of the most important Roman archaeological sites of Switzerland, although only a quarter of the Roman city has been excavated and is visible. The amphitheatre, the Grange des Dimes temple, the sanctuary of Cigognier, the theatre, the thermal complex, the city wall, the Tornallaz tower, the east and west gates and the Derrière la Tour palace are all accessible. The Roman museum, located in a medieval tower (11th century) in the amphitheatre, houses remarkable artifacts and gives a good overview of Celtic and Roman history. Due to its location on the Swiss plateau and at the crossroads of the north-south trade network, the city remained important even after the departure of the Romans in the fifth century. Avenches was even the seat of the bishop for a short time in the sixth century.
Medieval Avenches was founded by the Bishop of Lausanne in the thirteenth century, on a hill a few hundred meters from the ancient Roman city. The medieval buildings still dominate the city centre and the skyline. The Bishop of Lausanne also built the castle. Bern expanded it after the conquest of Vaud in 1536. The Renaissance façade and decorations are among the most beautiful in Switzerland. The city wall and the many medieval houses are in a fairly good condition, as are the rectory (1756) and the St. Marie-Madeleine church from the eleventh century. Other remarkable buildings are the town hall, the tower in the Roman amphitheatre, the Tour du Vully, the Tour du Montauban, the Tour de Benneville and the old hospital. In this respect, the city is still one of the most remarkable places in the former residential area of the Helvetii. Two thousand years ago, Aventicum had about 20,000 inhabitants, today about 4,500.